Atmospheric Environment (v.40, #12)

The daily municipal solid waste (MSW) generation in the Mexico City Metropolitan Area (MCMA) is the highest nationwide (∼26000 ton day−1); this amount is discarded in sanitary landfills and controlled dumps. Information about the type and concentration of potential pollutants contained in landfill gas (LFG) from these MSW disposal sites is limited. This study intends to generate information about the composition of LFG from five MSW disposal sites with different operational characteristics and stages, in order to identify their contribution as potential pollutant sources of total gaseous mercury (TGM) and volatile organic compounds (VOCs). Important methane (CH4) contents (>55%) in LFG were registered at three of the five sites, while two sites were found in semi-aerobic conditions (CH4<32%). Only at one site (a closed site), potentially polluting emissions from the LFG were detected, including toluene (∼90 ppm) and other VOCs, and especially high TGM concentrations (1100–1500 ng m−3). At the remaining sites, TGM levels in LFG were between 12.5 and 52.4 ng m−3. The impact of TGM contained in LFG emissions in ambient air was assessed by means of the TGMair/LFG ratio. This quotient indicated that values below 0.2, such as those found at two closed sites with final synthetic covers, could imply better closure practices than places with higher ratios, such as sites with only periodical clay cover. High values of the TGMair/LFG ratio were also related to external TGM sources of influence, as a landfill in operation stage located at a highly industrialized area.
Keywords: Landfill gas; Municipal solid waste; Disposal sites; Total gaseous mercury; Mexico City;

A process-oriented inter-comparison of a box model and an atmospheric chemistry transport model: Insights into model structure using α -HCH as the modelled substance by Kaj M. Hansen; Konstantinos Prevedouros; Andrew J. Sweetman; Kevin C. Jones; Jesper H. Christensen (2089-2104).
Two models that use different approaches to model the environmental distribution and fate of persistent organic pollutants (POPs) and feature different approaches to the description of environmental processes are compared. The European Variant Berkeley–Trent model (EVn-BETR) is a fugacity based box model using long-term averaged environmental input to drive inter-compartmental and inter-regional exchange processes. The POP version of the Danish Eulerian Hemispheric Model (DEHM-POP) is a 3-D atmospheric chemistry transport model using dynamic meteorological input to drive atmospheric transport and deposition to the surface. It is expanded with surface modules to describe the post-depositional re-emission processes of POPs. Seasonally averaged air, soil and water α -hexaclorocyclohexane ( α -HCH) concentrations and distribution patterns within the European region are compared for a number of emissions scenarios. There is generally a good agreement between the predicted distribution patterns of the two models. Discrepancies in environmental concentrations are attributed to the difference in efficiency of atmospheric removal processes arising from the differences in model parameterisation.
Keywords: Model inter-comparison; Dynamic models; Fugacity models; Atmospheric chemistry transport models; α -hexachlorocyclohexane;

Vapor pressure ( P vap ) is a fundamental property controlling the gas–particle partitioning of organic species. Therefore this pure substance property is a critical parameter for modeling the formation of secondary organic aerosols (SOA). Structure–property relationships are needed to estimate P vap because (i) very few experimental data for P vap are available for semi-volatile organics and (ii) the number of contributors to SOA is extremely large. The Lee and Kesler method, a modified form of the Mackay equation, the Myrdal and Yalkowsky method and the UNIFAC- p L o method are commonly used to estimate P vap in gas–particle partitioning models. The objectives of this study are (i) to assess the accuracy of these four methods on a large experimental database selected to be representative of SOA contributors and (ii) to compare the estimates provided by the various methods for compounds detected in the aerosol phase.
Keywords: Vapor pressure; Secondary organic aerosols; Gas–particle partitioning modeling; Structure–property relationship;

Local and regional contributions to springtime ozone in the Osaka metropolitan area, estimated from aircraft observations by Yasuyuki Itano; Shinji Wakamatsu; Shuichi Hasegawa; Toshimasa Ohara; Seiji Sugata; Masamitsu Hayasaki; Takeshi Moriya; Shinji Kobayashi (2117-2127).
Vertical profiles of springtime ozone (O3) over the Osaka metropolitan area in Japan were investigated by means of aircraft-based observations in March 2001 (Period I) and March 2003 (Period II). The observations in Period I were carried out during an episode of high O3 concentration under stagnant meteorological conditions, whereas in Period II, pollution levels were low and the weather was cloudy with strong winds. The elevated O3 concentration in the surface mixing layer in Period I was a result of local photochemical production as well as trans-boundary air pollution transported from East Asia. In contrast, the O3 concentration in Period II was very low, corresponding to the O3 level of ‘clean continental’ air masses from the northern Asian continent. On the basis of the vertical O3 profiles observed in Period I, we estimated the contributions of local photochemical production and trans-boundary air pollution to the O3 within the mixing layer, local photochemical production contributed −3% to 33% and trans-boundary air pollution contributed 8%–27%. We found that the trans-boundary air pollution made a notable contribution to the springtime O3 in the Osaka metropolitan area, its contribution being comparable to that of local photochemical production.
Keywords: Photochemical air pollution; Trans-boundary air pollution; Vertical profile;

The objective of this study was to characterize the emissions of air pollutants from mosquito coils and candles burning in a large environmental test chamber. The target pollutants included particulate matters (PM10, PM2.5), carbon monoxide (CO), nitrogen oxides (NO x ), methane (CH4), non-methane hydrocarbons (NMHC), volatile organic compounds (VOCs) and carbonyl compounds. The average PM10 concentrations for all tested mosquito coils exceeded Excellent and Good Classes objectives specified by Indoor Air Quality Objectives for Office Buildings and Public Places (IAQO) []. The emission factors (mg g−1 mosquito coil) of mosquito coils combustion were: PM2.5, 20.3–47.8; PM10, 15.9–50.8; CO, 74.6–89.1; NO, 0.1–0.5; NO2, n.d.–0.1; NO x , 0.1–0.5; CH4, n.d.–4.7; NMHC, 0.1–5.7. Formaldehyde and acetaldehyde were the most abundant carbonyls species in the coil smoke. The average concentrations of formaldehyde and benzene of all tested mosquito coils exceeded Good Class of IAQO. Nitrogen oxides were the most abundant gas pollutants relating to candle burning among all target air pollutants. The candle made of gel (CAN 4) would emit more air pollutants than the paraffin candles (CAN 1, 2 and 3) and beeswax candle (CAN 5). Among five candles tested, CAN 5, the one made of beeswax, generated relatively smaller amount of air pollutants. It was noted that the concentrations of most VOCs from candles combustion were below the detection limit.
Keywords: Environmental chamber; Emission factor; Candle; Mosquito coil; VOCs;

An investigation on NH3 emissions and particulate NH4 +–NO3 formation in East Asia by J.Y. Kim; C.H. Song; Y.S. Ghim; J.G. Won; S.C. Yoon; G.R. Carmichael; J.-H. Woo (2139-2150).
In this study, the accuracy of NH3 emissions in East Asia is evaluated by a comparison of measured and predicted NH4NO3 concentrations. For the prediction of particulate NH4NO3 concentrations, this study uses the USEPA Models-3/Community Multi-scale Air Quality (Models-3/CMAQ) model. The measurement data are collected from 4 ground-based stations (Beijing, Shanghai, Qingdao, and Kangwha) and ACE-ASIA C130 Flights #6, #7, and #10. The four ground-based stations and air flight tracks are located in and around the Yellow Sea in East Asia. According to the results, the predicted fine-mode NH4 +concentrations are 1.2–3.8 times overestimated compared to those measured on the mass basis, and fine-mode NO3 concentrations are 1.9–7.6 times overestimated on the mass basis. It is also revealed in this study that aberrantly high predicted fine-mode NO3 concentrations in East Asia can be attributed to the overestimated NH3 emissions. The predicted gas-phase NH3 concentrations and estimated NH3 emissions are likely to be 1.2–3.8 times overestimated in East Asia on the mass basis. Therefore, it is recommended that approximately 20–75% reduced NH3 emission fields should be used in future modeling studies for East Asia.
Keywords: NH3 emissions; NH4NO3 formation; Models-3/CMAQ model; East Asia;

Characterisation of traffic-generated particulate matter in Copenhagen by Peter Wåhlin; Ruwim Berkowicz; Finn Palmgren (2151-2159).
Fine and coarse fraction PM was simultaneously sampled with Dichotomous Stacked Filter Units at a road site and at an urban background site during both summer and winter periods. The collected mass was determined gravimetrically, and the contents of 26 elements were measured by Proton-Induced X-ray Emission (PIXE). NO x was monitored continuously at both sites. The road increments (road concentrations minus urban background concentrations) of PIXE elements, PM and NO x were analysed using the Constrained Physical Receptor Model (COPREM). Good agreement between the measured data and the model was achieved in both size fractions using four well-separated source profiles representing the emissions from exhaust, road/tyres, brakes and road salt. The analysis showed that the particles created by brake abrasion have aerodynamic diameters in the inhalable size range around 2.8 μm. This particle diameter is common mass median for a long list of heavy metals that are apportioned to the brakes source: Cr, Fe, Cu, Zn, Zr, Mo, Sn, Sb, Ba and Pb. Other significant contributions of Al, Si, K, Ca, Ti, Mn, Fe, Zn and Sr, mostly in the coarse particle fraction, are apportioned to the road/tyres source.
Keywords: Exhaust and non-exhaust traffic emissions; Source apportionment; Source profiles; Traffic emission factors; Emission of heavy metals;

Characterization of seasonal variation of tropospheric aerosols in Chiba, Japan by Shunsuke Fukagawa; Hiroaki Kuze; Gerry Bagtasa; Suekazu Naito; Masanori Yabuki; Tamio Takamura; Nobuo Takeuchi (2160-2168).
Seasonal variations of tropospheric aerosol properties in Chiba, Japan, are investigated by means of optical monitoring (1999–2005), ground sampling (1998–2004), and wind data. The observation site at Chiba University is located in the urban Chiba area, about 30 km southeast of Tokyo. The aerosol optical thickness (AOT) and Angstrom exponent are derived from the data taken with a sun photometer. The value of AOT at the wavelength of 500 nm exhibits a seasonal variation, showing small values (<0.2) in fall and winter, and large values (∼0.5) in spring and summer. The variation of Angstrom exponent is in the range 0.5–1.8, showing negative correlation with the wind speed. This indicates that the influence of anthropogenic particles from local sources becomes relatively important when the wind is weak near the ground level. The influence of Asian dust particles is also detected during March and April. The seasonal variation is remarkable also in the chemical analysis data. For fine particles with diameters less than 2 μm, elemental carbon dominates in fall and winter, while (NH4)2SO4 is prominent in spring and summer. For coarse particles, the fraction of sea salt particles increases in spring and summer.
Keywords: Seasonal variation; Optical thickness; Angstrom exponent; Aerosol chemical composition; Wind system;

Aerosol properties and radiative forcing in Hunshan Dake desert, northern China by Tiantao Cheng; Yan Liu; Daren Lu; Yongfu Xu; Hongyu Li (2169-2179).
Aerosol optical and radiative properties of Hunshan Dake (HD) desert were obtained from the ground-based sun/sky radiometer measurements at Sanggen Dalai, China, in the spring of 2001. The impacts of dust on the surface radiative balance were also examined by using the measurements of solar and infrared radiation. High aerosol optical thickness (AOT) mostly corresponded to the occurrence of dust events. The Angström exponent decreased with increasing AOT, and decreased to zero or negative when heavy dust events appeared in the HD desert. The size distributions of aerosols showed a tri-modal structure, one accumulation mode with radius near 0.1 μm and two modes of larger particles with radii 1.3–1.7 μm and 4.5–5.0 μm. For the total and coarse (r>0.6 μm) particles, the effective radius and volume radius increased with the aerosol content when the AOT was less than 0.6, but decreased with the aerosol content when the AOT was higher than 0.6. The real parts showed a behavior of low sensitivity to wavelength, 1.41–1.58 at 440, 670, 870 and 1020 nm. The imaginary parts also showed lower sensitivity to wavelength with a value of about 0.0007–0.0033 at the same four wavelengths. The absorption became a relative important component in extinction because of the effects of dust particles. The single scattering albedo performed little variation at four wavelengths, 0.97–0.99 for the fine (r<0.6 μm) particles and 0.90–0.98 for the coarse (r>0.6 μm) particles. The asymmetry factors also showed little variation with the increasing AOT, 0.61–0.72 at four wavelengths. In comparison with the clear days, the solar downward radiation decreased by about 51–69% and the infrared downward radiation increased by about 16–36% on dusty days on the surface. The dust of HD desert could lead to a temperature reduction on the surface depending on the offsetting combination of positive solar balance and negative infrared balance during daytime. The dust radiative forcing played an important role in the development of the dust event.
Keywords: Dust; Aerosol properties; Radiative forcing; Dust event; Hunshan Dake desert;

Organic and elemental carbon concentrations in carbonaceous aerosols during summer and winter sampling campaigns in Barcelona, Spain by M. Viana; X. Chi; W. Maenhaut; X. Querol; A. Alastuey; P. Mikuška; Z. Večeřa (2180-2193).
Daily PM10 and PM2.5 samples were collected at an urban background monitoring site in Barcelona (Spain) in summer and winter 2004. The instrumentation used consisted of two high-volume (PM10 and PM2.5) and two low-volume samplers (PM2.5), one of them coupled to an annular diffusion denuder aiming to evaluate the influence of sampling artefacts related to the adsorption of volatile carbonaceous species. Quartz fibre filters of 15 cm and 47 mm diameter were used as collection substrates (Schleicher & Schuell QF20 and Whatman QM-A, respectively). The resulting samples were analysed for organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC). Total carbon (TC) was calculated as OC+EC. The present study aimed to (a) determine maximum (winter) and minimum (summer) OC/EC/TC/WSOC levels in the study area, and (b) assess the magnitude and influence of positive sampling artefacts. Mean levels of TC in PM2.5 ranged from 4 to 5 μg m−3 in summer to 7–10 μg m−3 in winter with the different samplers (5 and 8 μg m−3, respectively, in PM10, one sampler); OC levels in PM2.5 were 3–4 μg m−3 in summer and 6–7 μg m−3 in winter (4 and 6 μg m−3 in PM10); EC levels in PM2.5 ranged from 1 to 2 μg m−3 in summer to 1–3 μg m−3 in winter (1 and 2 μg m−3 in PM10). Thus, OC/EC/TC winter levels were higher than summer levels by a factor of 1.7–2. WSOC levels were 1.6 μg m−3 in PM2.5 and PM10 in summer, and 2.1 μg m−3 (PM2.5) and 1.9 μg m−3 (PM10) in winter. The results indicate that positive artefacts for OC accounted for 0.5–0.7 μg m−3, representing 11–16% of the raw OC mass and 3% of the PM2.5 mass. Sampling artefacts for OC were slightly higher in summer. EC levels were similar for the low-volume samplers and unusually low for the high-volume samplers, suggesting that EC determination could be influenced by the filter type.
Keywords: Sampling artefacts; Annular diffusion denuder; OC/EC; WSOC; Urban aerosols; Traffic;

Mercury concentrations in size-fractionated airborne particles at urban and suburban sites in Beijing, China by Zhangwei Wang; Xiaoshan Zhang; Zuoshuai Chen; Yi Zhang (2194-2201).
Mercury concentrations in size fractions of airborne particulate matter obtained from urban and suburban sites in Beijing in 2003 and 2004 are presented in this paper. The average concentrations of total particulate mercury were 1.18±0.82 ng m−3 with a range of 0.18–3.51 ng m−3at the urban site and 0.68±0.62 ng m−3 with a range of 0.13–2.40 ng m−3 at the suburban site. This is much higher than what is found in Europe and Northern America. The results implie that significant anthropogenic sources in Beijing contribute to the concentration of particulate mercury in air and therefore, to the mercury deposition in this region. There are clear seasonal variations in concentration of particulate mercury with highest concentrations in winter at urban and suburban sites. This illustrates the important contribution from coal burning to particulate mercury during the heating season. The mercury concentration in each size fraction of airborne particulates was closely related to its size range. The highest mercury concentration was found in the size fraction less than 1.1 μm with average concentrations of 0.59±0.50 and 0.29±0.26 ng m−3 at the urban and suburban sites, respectively. The mercury in this size fraction accounts for 45.7±9.5% and 41.9±8.2% of the total particulate mercury, respectively. This implies that a large fraction of the particulate mercury in this area can be transported long range before it becomes deposited. Based on the concentrations of size-fractionated particulate mercury in ambient air, the dry deposition fluxes of mercury were estimated to 407 μg m−2  a−1 at the urban site and 270 μg m−2  a−1 at the suburban site. More than 90% of the deposition flux came from particles larger than 1.1 μm despite a substantial fraction of the Hg found in particles less than 1.1 μm.
Keywords: Mercury; Airborne particulates; Beijing; China;

Estimating contributions of indoor and outdoor sources to indoor carbonyl concentrations in three urban areas of the United States by W. Liu; J. Zhang; L. Zhang; B.J. Turpin; C.P. Weisel; M.T. Morandi; T.H. Stock; S. Colome; L.R. Korn (2202-2214).
Exposure to carbonyls (aldehydes and ketones) can produce adverse health effects. It is known that various sources of carbonyls are often present inside residences but little is known about their indoor source strengths. In the present paper, we used a database established in the relationships of indoor, outdoor, and personal air (RIOPA) study to estimate indoor source strengths of 10 carbonyls and outdoor contributions to measured indoor concentrations of these carbonyls. We applied a mass balance model to analyze paired indoor and outdoor carbonyl concentrations simultaneously measured in 234 RIOPA homes. Among all the measured carbonyls, formaldehyde, and acetaldehyde had the strongest indoor source strengths with the estimated median values of 3.9 and 2.6 mg h−1, respectively. Hexaldehyde also had large indoor source strengths with a median of 0.56 mg h−1. Acetone had the largest variations in indoor source strengths ranging from undetected to 14 mg h−1. The medians of the estimated indoor source strengths were 0.15 mg h−1 for propionaldehyde, 0.18 mg h−1 for glyoxal, 0.17 mg h−1 for methylglyoxal, and 0.23 mg h−1 for benzaldehyde. Acrolein and crotonaldehyde had the weakest indoor source strengths with no indoor sources detected in the majority of the RIOPA homes that were selected to have only nonsmoker residents. Consistent with the indoor source strength results, our estimated outdoor contributions to indoor concentrations were low for formaldehyde. In contrast, more than 90% of the indoor concentrations for acrolein and crotonaldehyde were from outdoor sources. The outdoor contributions to indoor concentrations for acetone, propionaldehyde, benzaldehyde, glyoxal, and methylglyoxal ranged from 10 to 90% across the RIOPA homes, suggesting that both indoor and outdoor sources had contributions to indoor concentrations of these compounds.
Keywords: Carbonyls; Aldehydes; Source strength; Indoor/outdoor ratios; Indoor air quality; VOC exposure;

Speciation and mass distribution of mercury in a bituminous coal-fired power plant by Sung Jun Lee; Yong-Chil Seo; Ha-Na Jang; Kyu-Shik Park; Jeom-In Baek; Hi-Soo An; Kwang-Chul Song (2215-2224).
Characterization and mass balance of mercury in a coal-fired power plant were carried out in a 500 MW, bituminous coal consuming electric utility boiler. This facility is equipped with a cold-side electrostatic precipitator (ESP) and a wet flue gas desulfurization (FGD) in series as air pollution control devices (APCDs). Mercury sampling points were selected at both the up and down streams of the ESP and outlet of the FGD, which is at stack. Two different types of sampling methods were employed, one is the Ontario Hydro (OH) method (ASTM D6784) and the other is US EPA101A. Various samples were collected from the coal-fired power plant such as fuel coals, fly ash in hopper, lime/lime stone, gypsum, and effluent water from FGD. These samples were analyzed by US EPA 7470A and 7471A to understand the behavior and mass balance of mercury in the process of a coal-fired power plant. There are no significant differences between the two sampling methods, but the OH method seems to have more advantages for Hg sampling from a coal-fired power plant because mercury speciation is quite an important factor to estimate the mercury emission and control efficiency from combustion flue gas. Approximate Hg mass balance could be obtained from various samples in the study; however, a series of long-term and comprehensive study is required to evaluate the reliable Hg mass distribution and behavior in a coal-fired power plant.
Keywords: Mercury; Coal-fired power plant; Flue gas control; Mass balance; Mercury speciation;

Measurements of nitrous oxide emissions from vegetable production in China by Zhengqin Xiong; Yingxin Xie; Guangxi Xing; Zhaoliang Zhu; Chris Butenhoff (2225-2234).
Nitrous oxide (N2O) emissions resulting from Chinese vegetable production were measured. A site in suburban Nanjing (East coast; Jiangsu Province) was monitored from November 2001 to January 2003, in which five consecutive vegetable crops were sown. The crops consisted of radish, baby bok choy, lettuce, second planting of baby bok choy, and finally celery. Results suggested that N2O emission events occur in pulses. The average N2O-N flux for all five crops was 148±9 μg N m−2  h−1 and the average emission rate was 12±0.7 kg N ha−1. The average seasonal emission fluxes ranged from 37 μg N m−2  h−1 in the radish plot to 300 μg N m−2  h−1 in the celery plot. The celery field produced the greatest cumulative emission of 5.8 kg N ha−1 while the baby bok choy field had the lowest rate of 0.96–1.0 kg N ha−1. In total, 0.73% of applied fertilizer N was emitted as N2O-N as a whole. The lettuce field had the largest emission factor of 2.2%. Results indicate that emissions from vegetable field are a potential source of national N2O inventory.Temporal variation is much greater than spatial variation and the corresponding CV averaged 115% and 22%, respectively. Under the same total sampling quantity, increasing sampling frequency is more important than increasing spatial replicates.
Keywords: Crop system; Tillage management; Nitrogen source; Emission factor; Sampling strategy;

Nitrogen oxides (NO x =NO+NO2) are a common group of nitrogen-containing trace gases that interact significantly with plant canopies and play a critical role in atmospheric chemistry including the formation of ozone, smog and nitric acid. The controls over leaf–atmosphere exchange of NO x (NO x =NO+NO2) have been characterized for a few plant species and important drivers have been identified including stomatal conductance, the partial pressure gradient from the interior to the exterior of the leaf, and, most recently the level of ultraviolet radiation. However, our ability to predict leaf fluxes has been hampered by a dearth of information describing the reactions occurring between NO x and internal constituents of the leaf (often referred to as the mesophyllic resistance). In this study, we investigated NO x uptake in four important agricultural plant species and specifically tested the hypothesis that ascorbic acid within the leaf was a significant control over mesophyllic resistance. Measurements were made using a dynamic leaf chamber at ambient mixing ratios typical of urban atmospheres. Measured NO and NO2 leaf fluxes were lower than the potential flux calculated assuming stomatal conductance as the sole limitation (i.e., no mesophyllic resistance). The ratios of leaf intercellular to ambient concentrations ( C i / C a ) for NO across partial pressures and plant species was usually >0.99 and the leaf uptake rates of NO were negligible within the ranges examined. In contrast, leaf uptake for NO2 was much greater and C i / C a were often as low as 0.75. For both gases, C i / C a ratios>1 were observed at low ambient mixing ratios indicating emission from leaves. Across plant species, plants with higher leaf nitrogen contents showed higher NO2 emission rates and plants with higher leaf ascorbate concentrations had higher leaf NO2 uptake rates. These results suggest that in addition to the known effects of stomatal conductance and incident UV radiation, leaf nitrogen content and the capacity for the scavenging of NO x by ascorbic acid may explain the variation in the ability of plants to absorb atmospheric nitrogen oxides.
Keywords: Nitric oxide; Nitrogen dioxide; Conductance; Ascorbic acid;